Chemically sensitizing photographic silver halide emulsions with phosphonium compounds



United States Patent O CHEMICALLY SENSITIZING PHOTOGRAPHIC SIL- VER HALIDE EMULSIONS WITH PHOSPHONIUM COMPOUNDS Wesley G. Lowe and Arthur H. Herz, Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed Mar. 10, 1967, Ser. No. 622,044

Int. Cl. G03c 1/28 US. Cl. 96-107 Claims ABSTRACT OF THE DISCLOSURE Sensitizing photographic silver halide emulsions with phosphonium salts of the formula RoH),P+z

wherein R is an alkyl group and wherein Z is an anion.

BACKGROUND OF THE INVENTION Field of the invention Description of the prior art It is known that silver halide emulsions can be sensitized with a variety of materials as a means of incerasing the speed and contrast of the emulsion as opposed to optical sensitization in which the optical range of sensitivity is increased. In increasing sensitivity, however, many prior art sensitizers also increase the residual fog. It would be desirable to have a chemical sensitizer which does not increase the residual fog.

SUMMARY OF THE INVENTION According to our invention, we have found that photographic silver halide emulsions can be sensitized with certain phosphonium compounds conforming to the following formula:

wherein each R represents an alkyl group which may be the same or a different alkyl group, substituted or unsubstituted, and Z represents any anion which does not exhibit a deleterious effect in a photographic system. Preferably, R represents a lower alkyl group such as methyl, ethyl, propyl, or butyl and Z represents anions such as nitrate, perchlorate, halides, e.g., chloride, bromide, or iodide, etc.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The sensitizers of our invention can be employed in any concentration suitable for the intended purpose. Good sensitization is generally achieved when the phosphonium salts are employed in a concentration of from about 0.01 to about 10, preferably about 0.05 to about 3, milligrams per mole of silver in the silver halide emulsion.

Preferred compounds falling within the above formula are tetrakis(hydroxymethyl)phosphonium salts and tetrakis(hydroxyethyl)phosphonium salts. Examples of these salts are tetrakis(hydroxymethyl)phosphonium chloride (THPC manufactured by Hooker Chemical Company) and tetrakis(hydroxyethyl) phosphonium chloride. The latter compound can be obtained by the procedure described in Messenger and Engles, Ber. 21: 326 (1888). The general equation for the production is It is believed that our tetrahydroxyalkyl phosphonium salts sensitize by forming a phosphine which acts as the reducing species. Alkyl phosphines per se cannot conveniently be used directly since they undergo aerial oxidation and therefore are unstable.

Our sensitizers can be added in a variety of ways to photographic systems and at various stages in the preparation thereof. In general, with respect to silver halide emulsions, the sensitizers can be added with useful effects at the completion of the Ostwald ripening and prior to one or more of the final digestion operations. The sensitizing addenda are preferably added to silver halide emulsions after the silver halide grains are substantially in their final size and shape. The addenda can be added in the form of their aqueous solutions, where they are soluble in water, or in an innocuous organic solvent where the sensitizer does not have sufficient solubility in water to be used in the form of an aqueous solution.

Vacuum-deposited photographic systems substantially free of conventional vehicles, binders or dispersing agents can also be sensitized in accordance with the instant invention by incorporating the sensitizers in a coating or layer contiguous to the vacuum-deposited light-sensitive material.

The silver halide emulsion of a photographic element which can be sensitized according to this invention can contain conventional addenda such as gelatin plasticizers, coating aids, antifoggants such as the azaindines and hardeners such as aldehyde hardeners, e.g., formaldehyde, mucochloric acid, glutaraldehyde bis(sodium bisulfite), maleic dialdehyde, aziridines, dioxane derivatives and oxypolysaccharides. Sensitizing dyes useful in sensitizing such emulsions are described, for example, in US. Pat. 2,526,- 632 of Brooker and White issued Oct. 24, 1950, and 2,503,776 of Sprague issued Apr. 11, 1950. Spectral sensitizers which can be used are the cyanines, merocyanines, complex (trinuclear) cyanines, complex (trinuclear) merocyanines, styryls and hemicyanines. Developing agents can also be incorporated into the silver halide emulsion if desired or can be contained in a separate underlayer. Various silver salts may be used as the sensitive salt such as silver bromide, silver iodide, silver chloride, or mixed silver halides such as silver chlorobrornide or silver bromoiodide.

The silver halide emulsion layer of a photographic element which can be sensitized according to the instant invention can contain any of the hydrophilic water-permeable binding materials suitable for this purpose. Suitable materials include gelatin, colloidal albumin, polyvinyl compounds, cellulose derivatives, acrylamide polymers, etc. Mixtures of these binding agents can also be used. The binding agents for the emulsion layer of the photographic element can also contain dispersed polymerized vinyl compounds. Such compounds are disclosed, for example, in US. Pats. 3,142,568 of Nottorf issued July 28, 1964; 3,193,386 of White issued July 6, 1965; 3,062,674 of Houck, Smith and Yudelson issued Nov. 6, 1962; and 3,220,844 of Houck, Smith and Yudelson issued Nov. 30, 1965; and include the water-insoluble polymers of alkyl acrylates and methacrylates, acrylic acid, sulfoalkyl acrylates or methacrylates and the like.

The silver halide emulsion of a photographic element which can be sensitized according to the instant invention can be coated on a wide variety of supports. Typical supports are cellulose nitrate film, cellulose ester film, polyvinyl acetal film, polystyrene film, poly(ethylene terephthalate) film and related films or resinous materials as well as glass, paper, metal and the like. Supports such as paper which are coated with a-olefin polymers, particularly polymers of a-olefins containing two or more carbon atoms, as exemplified by polyethylene, polypropylene, ethylene-butene copolymers and the like can also be employed.

The speed of photographic emulsions sensitized according to the invention can be further increased by including in the emulsions a variety of hydrophilic colloids, such as carboxymethyl protein of the type described in U.S. Pat. 3,011,890 of Gates, Jr., Miller and Koller issued Dec. 5, 1961, and polysaccharides of the type described in Canadian Pat. 635,206 of Koller and Russell issued J an. 2.3, 1962.

Photographic emulsions sensitized according to the invention can contain speed increasing compounds such as quaternary ammonium compounds, polyethylene glycols or thioethers. Frequently, useful eifects can be obtained by adding the aforementioned speed increasing compounds to the photographic developer solutions in stead of, or in addition to, the photographic emulsions.

Photographic elements sensitized according to the invention can be used in various kinds of photographic systems. In addition to being useful in X-ray and other non-optically sensitized systems, they can also be used in orthochromatic, panchromatic, and infrared sensitive systems. The sensitizing addenda can be added to photographic systems before or after any sensitizing dyes which are used.

Silverhalide emulsions sensitized according to the in- 'vention can be used in color photography, for example, emulsions containing color-forming couplers or emulsions to be developed by solutions containing couplers or other color-generating materials, emulsions of the mixed-packet type, such as described in Godowsky U.S. Pat. 2,698,794 issued Jan. 4, 1955; in silver dye-bleach systems; and emulsions of the mixed-grain type, such as described in U.S. Pat. 2,592,243 of Carroll and Hanson issued Apr. 8, 1952.

Other sensitizers can be employed in combination with the sensitizers of the invention, e.g., naturally active gelatin, sulfur, selenium, tellurium and/or gold compounds, salts of noble metals of Group VIII of the Periodic Table which have an atomic Weight greater than 100, etc.

The following examples will illustrate the invention but are not to be construed to limit it in any way.

EXAMPLE 1 A fine-grain, low-gelatin, positive emulsion is pre- Relative Sensitizer (mgJAg mole) Speed Gamma Fog None (control) 100 0. 54 0. (CH2OH)4P+C1" (0.10) 200 1. 24 0. 05 (CH2OH)4P+C1- (0.25) 320 2. O8 0. 05 (CH2OH)4P CI (0.50) 630 2. 28 0 06 4 EXAMPLE 2 Portions of an emulsion prepared according to the method of Example 1 are sensitized with various compounds listed below by holding the emulsion containing the compounds for 30 minutes at 60 C. The emulsions are then coated, exposed and developed in the same mannor as in Example 1 with the following results Relative Sensitizer (mg/Ag mole) Speed Gamma Fog None (control) 0. 44 0. 05 (OH2OH)4P+CI- (0.25) 2.12 0. 08 Sodium thiosulfate (7) 1, 590 2. 50 0. 18 (C(l7i2OH)4P+Gl-' (0.25) plus sodium thiosulfate 2, 520 2. 72 0.22

EXAMPLE 3 Portions of an emulsion prepared according to the method of Example 1 are sensitized with varying amounts of tetrakis(hydroxyethyl)phosphonium chloride by holding the emulsion containing the sensitiz/er for 60 minutes at 40 C. and 60 C. The emulsions are then coated, exposed and developed in the same manner as in Example 1 with the following results:

sensitizing, Rela- Temperativ Sensrtrzer (mg/Ag mole) ture (*C.) Speed Gamma Fog None (control) 1. 47 0. D5 (CHaCHOH)4P+Cl- (0.10) 40 126 2. 02 0. 05 (CHaOHOHhP Cl (0.25) 40 224 2. 58 0. 05 (CHaCHOH)4P+Cl- (0.10) 60 2.14 0. 07 (GHQCHOHMPKJI- (0.25) 60 364 2. 20 0. 09

wherein each R is a lower alkyl group and Z is an anion.

2. The emulsion of claim 1 wherein said compound is present in a concentration of from about 0.01 to about 10 milligrams per mole of silver in said silver halide emulsion.

3. The emulsion of claim 2 wherein said compound is a tetrakis(hydroxymethyl)phosphonium salt or a tetrakis(hydroxyethyl) phosphonium salt.

4. The emulsion of claim 3 wherein said compound is tetrakis(hydroxymethyl)phosphonium chloride.

5. The emulsion of claim 3 wherein said compound is tetrakis(hydroxyethyl)phosphonium chloride.

6. A photographic element comprising a support coated with the emulsion of claim 1.

7. A photographic element comprising a support coated with the emulsion of claim 2..

8. A photographic element comprising a support coated with the emulsion of claim 3.

9. A photographic element comprising a support coated with the emulsion of claim 4.

10. A photographic element comprising a support coated with the emulsion of claim 5.

11. A process comprising sensitizing an unexposed silver halide emulsion with a compound of the formula:

wherein each R is a lower alkyl group and Z is an anion comprising adding a chemical sensitizing concentration of said compound to said emulsion and heating said emulsion.

12. The process of claim 11 wherein said compound is present in a concentration of from about 0.01 to about 10 milligrams per mole of silver in said silver halide emulsion.

13. The process of claim 12 wherein said compound is a tetrakis(hydroxymethyl)phosphonium salt or tetrakis(hydroxyethyDphosphonium salt.

14. The process of claim 13 wherein said compound is tetrakis (hydroxymethyl)phosphonium chloride.

15. The process of claim 13 wherein said compound is tetrakis(hydroxyethyl)phosphonium chloride.

References Cited 5 UNITED STATES PATENTS 2,271,622 2/1942 Carroll et al 96-107 XR NORMAN G. TORCHIN, Primary Examiner 10 R. E. FIGHTER, Assistant Examiner 

